Digital signals are transmitted via synchronous networks, corresponding to the SDH or SONET standard. In this case, the useful data are transmitted with a so-called STM-1 transport module. The latter includes the useful data and additional overhead information.
A number of lower-order STM-M signals, such as, for example, STM-1, are combined by time division multiplexing to form a higher-order STM-N signal, in order to achieve efficient channel utilization. In this case, the overheads of the lower-order STM-M signals are evaluated and a new overhead of the higher-order STM-N signal is formed.
Overhead information and signal defects, such as alarm messages and bit errors which are contained in the incoming tributary signal (STM-M), are transmitted non-transparently in a conventional SDH/SONET system, since this is not provided according to the SDH/SONET standard due to the termination of line sections.
However, in contrast to the standard method, the operator of a transport network demands that data channels that are as transparent as possible be made available to its customers.
Such a transparent method for SDH/SONET signals has not yet been standardized at the present time.
An object to which the present invention is directed consists in transmitting overhead information and signal defects of lower-order SDH/SONET signals via a higher-order SDH/SONET multiplex signal.
A further object of the present invention is to evaluate the signal defects of the tributary signals and the signal defects of the higher-order multiplex signal and assign them to the associated outgoing tributary signals.